The present invention relates to a new and improved construction of a cooling apparatus for cooling an object by means of expanding a pressurized gas which is precooled below its inversion temperature; the pressurized, precooled gas is passed through a depressurization outlet and thereby expanded in a manner such that a gas jet exits from the depressurization outlet and is directed towards a surface of the object to be cooled.
In a cooling apparatus such as known, for example, from British Patent No. 1,238,911, published Jul. 14, 1971, cooling is achieved by means of a pressurized gas which is expanded or depressurized by being passed through a nozzle For this purpose, the gas must have a temperature below its inversion temperature prior to expansion or depressurization. In order to accomplish this, the cooling apparatus according to British Patent No. 1,238,911 is equipped with two coolers. In a first one of the two coolers a first gas is conducted in the gaseous state from a source of pressurized gas along a first path of a countercurrent heat exchanger, expanded or depressurized through the nozzle and returned along a second path of the heat exchanger in countercurrent fashion As a result, the forward flowing pressurized gas is cooled. The second one of the two coolers causes precooling of the first gas prior to arrival at the countercurrent heat exchanger of the first cooler In this arrangement, the second cooler receives a pressurized liquid which is sprayed into a chamber through a nozzle. During this operation, the liquid evaporates whereby the cooling action of the second cooler is provided The first cooler of this arrangement serves to cool an object in the form of an infrared detector.
German Published Patent Application No. 3,642,683, published Jun. 16, 1988, and cognate with U.S. Pat. No. 4,819,451, granted Apr. 11, 1989, describes a cryostat for cooling an infrared detector and which cryostat is based on the Joule-Thomson effect A countercurrent heat exchanger includes a forward or infeed conduit and is placed in a Dewar vessel. The forward or infeed conduit terminates in an expansion or depressurization nozzle. The infrared detector is placed at an end wall inside the Dewar vessel. A heat insulating layer is arranged between the Dewar vessel and a base in order to reduce the heat load. In order to improve the cooling power of the Joule-Thomson process achievable at a predetermined mass flow of the pressurized gas, an inlet end of the forward or infeed conduit is cooled by means of Peltier elements.
German Published Patent Application No. 1,502,715, published Oct. 30, 1969, shows an apparatus for liquifying a gas. The apparatus includes two expansion coolers; a first one of the two expansion coolers is operated using hydrogen whereas a second one of the two expansion coolers is operated using air or nitrogen. Both the two expansion coolers are constructed as Joule-Thomson coolers, i.e. contain a countercurrent heat exchanger in which the respective expanded or depressurized and cooled gas enters into heat exchange with the forward flowing or infed gas. The liquid nitrogen or liquid air which is obtained by means of the second Joule-Thomson cooler serves for precooling the hydrogen present in the first Joule-Thomson cooler. The hydrogen is thereby cooled below its inversion temperature. However, the nitrogen can be cooled by means of the respective Joule-Thomson cooler only down to the boiling point of nitrogen.
A similar arrangement is shown in German Published Patent Application No. 1,501,106, published on Jan. 8, 1970.
European Published Patent Application No. 0,271,989, published on Jun. 22, 1988, describes using, in a conventional single-stage Joule-Thomson cooler, a coolant comprising a mixture of nitrogen, argon or neon and methane, ethane or propane with the addition of combustion inhibiting materials like bromotrifluoromethane.
German Published Patent Applications Nos. 3,337,194, published on Apr. 25, 1985, and 3,337,195, published on Apr. 25, 1985, British Published Patent Application No. 2,119,071, published on Nov. 9, 1983, and European Published Patent Application No. 0,234,644, published on Sep. 2, 1987, illustrate the use of single-stage Joule-Thomson coolers for cooling electronic or opto-electronic components.
With respect to gyro-stabilized seekers including image resolving detectors, German Published Patent Application No. 3,925,942, published Feb. 14, 1991, and cognate with U.S. Pat. No. 5,077,465, granted Dec. 31, 1991, suggests arranging the seeker at a carrier which is aligned to the gyro rotor axis and thus to the optical axis of the imaging optical system so that, even in the case of "squinting" of the seeker, the plane of the planar detector constantly extends perpendicular to this optical axis. In this arrangement the problem exists of cooling the detector. In the Joule-Thomson coolers which are usually employed for cooling detectors, there is provided a countercurrent heat exchanger through which the expanded or depressurized gas is returned whereby the inflowing gas is precooled by the gas return flow. The expanded or depressurized gas should be utilized as completely as possible for the precooling operation. Losses of gas and heat must be avoided. This can be achieved when the detector is fixedly arranged in the Dewar vessel Problems, however, occur when the detector is mounted at a movable carrier.
German Published Patent Application No. 3,941,314, published on Jun. 20, 1991, and cognate with U.S. Pat. No. 5,150,579, granted Sep. 29, 1992, describes a cooling apparatus for cooling a pivotable detector using a first cooler which comprises an expansion or depressurization nozzle. Pressurized argon which has been precooled below its inversion temperature, is expanded or depressurized with cooling by passing the same through the expansion or depressurization nozzle. The argon precooling is effected by means of a second cooler which is operated using methane The second cooler constitutes a Joule-Thomson cooler including an expansion or depressurization outlet through which the pressurized methane is expanded or depressurized with cooling. A heat exchanger precedes the expansion or depressurization outlet and serves for precooling the infed methane by the cooled, expanded or depressurized methane. The first cooler, however, constitutes an expansion cooler including an expansion or depressurization outlet preceded by a heat exchanger in which the pressurized argon is in heat exchange only with the expanded and cooled methane The argon which issues from the expansion or depressurization outlet of the first cooler, is expanded or depressurized and cooled down to its boiling point and directed in the form of a jet towards the object to be cooled.